The Application And Micro-Mechanism Of Carbonated Reactive Magnesia Solidified Soils

The application of accelerated carbonation in the ageing of reactive magnesia (MgO) stablised soils is an innovative low carbon method for soft soil treatment. In order to study the application and the micro-binding mechanism of MgO carbonated soils, a silt in Suqian, two silty clays in Nanjing and Haian were used. The binder used in this study is reactive MgO and CO2. Samples were made by static pressured and carbonized in a cylindrical carbonation device. The main results obtained from laboratory tests, microstructure test and theory analysis are as follows:(1) The influence of initial soil density, water content, soil properties and carbonation curing time on the carbonation strengthing effects of MgO solidified soils were studied by testing the dry density, the water content, pH value and soil particle distribution of these samples. The results show that:(1) With the increase of carbonation time, the water content and pH value of MgO solidified soils decreased gradually, the dry density of which increased and then levelled off after 6 hours’carbonation; the clay content increased when the silt and sand content increased of MgO solidified soils after carbonation. With the increase of soils’initial density, the dry density of three types of carbonated soil samples increased gradually; the water content of three types of soil samples increased with the increasing initial water content after carbonation. For Suqian silt, the water content of samples increased first and then decreased with the increase of soils’initial density, and the dry density of samples increased and then levelled off with the increase of the initial water content, while the pH values of samples decreased and then increased with the increase of the initial water content. For Nanjing silty clay and Haian silty clay, the water content of samples did not show any obvious changees with the increase of soils’initial density, and the dry density of sampes decreased with te increase of initial water content, while the pH values of carbonated Nanjing silty clay samples and carbonated Haian silty clay samples did not show any significant changes with the increase of the initial water content.(2) The change of mineral composition and microstructure under the influence of the initial density, the water content and carbonation time is studied. In addition, a carbonation reaction model of silt and silty clay was introduced here. The test results show that:Nesquehonite, hydromagnesite and dypingite are the main carbonation products of MgO solidified samples. The uncarbonated brucite increased with the increase of the initial water content of carbonated samples.With the increase of the carbonation time, the carbonation products were increased, and the strength of solidified soils increased along with the improved chemical cementation and filling effect. The cumulative pore volume of MgO solidified soils reduced gradually after carbonation. The porosity and mean pore size decreased gradually with the increasing carbonation time. The porosity and mean pore size increased with the increasing initial water content.(3)The carbonation reaction model of silt and silty clay was introduced to determine the shortest carbonation time of solidified soils. The strength of silt reaches the highest after 3 hours’ carbonization, while the strength of cilty caly reaches the highest after 6-12 hours’ carbonization.(4)An initial study of the carbonation construction process was carried out by studing the chamber tested samples. The results show that the cover pipe carbonization process can carbonate MgO solidified soft soil in-situ, and the strength of MgO solidified silt after carbonation was found significantly higher than that of plain soil.